Research On Physical-layer Network Coding And Cooperative Relay Selection Strategy

With the large-scale popularity of the Internet and the rapid development of mobile communication, which bring much convenience for us. For the radio characteristics of wireless channel, on the one hand, we can use this feature to improve the reliability of communication by cooperative relay, and the physical-layer network coding is a hot topic in research; on the other hand, we also need to consider security. Physical-layer security is considered as a promising solution towards absolute security in communication systems, it seems the most tightly security policies. In this situation, physical-layer security has attracted more and more attention to researches. In addition, more and more applications widely realized with the aid of relay network, cooperative relay selection has already been a hot topic in wireless communication research field. This work mainly investigated the physical-layer network coding subjected to the asymmetric channels, relay selection scheme for physical layer security, and relay selection criterion under outdated channel state information.Firstly, the performance of physical layer network coding under asymmetric two-way relay channels is studied. According to different cases: phase asymmetry, downlink asymmetry, uplink asymmetry and node asymmetry, analyzed the bit error rate performance of the physical-layer network coding, and compared with symmetric channel situation. Analytical and simulation results show that the bit error rate performance of phase downlink asymmetry is the best case; phase uplink asymmetry and node asymmetry are taken second place; downlink asymmetry and uplink asymmetry are the worst cases. As the bit error rate is 10-3, the difference between the SNR for the symmetry and the phase downlink asymmetry is 0.5 d B, the symmetry is less 1.5 d B than downlink asymmetry, and less 2.2 d B than uplink asymmetry.Secondly, the issue of physical security for cognitive radio networks is investigated. The achievable secrecy rate and secrecy outage probability have been analyzed in terms of conventional relay selection, direct transmission and optimal relay selection scheme. On the basis of the expression of secrecy rate and secrecy outage probability for conventional relay selection, the secrecy outage probabilities for direct transmission with three different cases(with one eavesdropper, with multiple eavesdroppers, with multiple primary users) are studied. Similarly, we analyzed the optimal relay selection scheme. In the high SNR region, the asymptotic approximations of the secrecy outage probability of the above three different strategies are also derived. We analyzed the corresponding relationships between secrecy rate and secrecy outage probability with transmitted power by numerical simulation. Simulation results show that the performance of one eavesdropper is superior to the multiple eavesdroppers; one primary user is superior to the multiple primary users.Finally, the impact of outdated CSI for opportunistic two-relay cooperative system is analyzed. For the optimal relay might be unavailable due to various reasons in the real system, a simple thN best-relay selection criterion is proposed. The outage probability performance of the thN best-relay selection scheme under the outdated CSI is investigated, and a tight closed-form lower bound and asymptotic value of the outage probability over Rayleigh fading channels are derived. Analytical and Simulation results demonstrate that the theoretical results of the outage probability very closely matches with Monte Carlo simulated ones, and the asymptotic results provide good tight approximations to the simulation ones in the high SNR region.